Download 2. OS Components

Operating System Services
• An operating system provides an environment for the execution of
programs.
• It provides certain services to programs and to the users of those
programs.
Operating System Components
• To provide the services and to manage the system the OS should have the
appropriate programs or modules.
• Those are called the components of OS.
The Operating System programs consist of the following set of programs
OS Components
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Process Management
Main Memory Management
I/O System Management
File Management
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Protection System
Networking
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Secondary-Storage Management
Command-Interpreter System
Process Management
A process is a program in execution
A process needs certain resources, including CPU time, memory, files, and I/O devices,
to accomplish its task
The operating system is responsible for the following activities in connection with
process management
Process creation and deletion
Process suspension and resumption
Provision of mechanisms for:
process synchronization
process communication
OS
Process manager
Process
suspension or
termination
Creation of
Processes
Making
Decision
which
processes
and when to
run
CPU
Main-Memory Management
Main memory is the only place where the program is loaded to run. It should be used
effectively to fit as many programs as possible
The operating system is responsible for the following activities with the memory
management
Keep track of which parts of memory are currently being used and by whom
Decide which processes to load when memory space becomes available
Allocate and deallocate memory space as needed
OS (Memory manager)
Memory
Processes
Making
Decision
which
processes
and where
to place
File Management
A file is a collection of related information defined by its creator.
The operating system is responsible for the following activities with the file
management:
Files, Directories creation and deletion
Support of basic methods for manipulating files and directories
OS (File manager)
Programs
Suggesting universal methods of:
- file access (sequential, random)
- file organization (directory tree).
HDD,
Tape,
Flash Disk,
Floppy disk,
CDROM
I/O System Management
I/O subsystem hides the peculiarities of specific hardware devices from the user.
The I/O system consists of:
A buffer, caching, spooling system
A general device-driver interface
Drivers for specific hardware devices
OS (Device Drivers)
Programs
Suggesting universal
methods of I/O devices
access.
HDD, Tape,
Flash Disk, Floppy
disk, CDROM,
Printer, Scanner,
Keyboard
Secondary (Mass) Storage Management
The operating system is responsible for the following activities with disk management:
Free space management
Storage allocation
Disk scheduling
OS (Mass Storage Manager)
Programs
Suggesting effective
methods of Mass
Storage usage.
HDD,
Tape,
Flash Disk,
Floppy disk,
CDROM
Networking
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A distributed system collects physically separate, possibly heterogeneous, systems into a
single coherent system,
providing the user with universal access to the various resources that the system maintains
(like OSI layers).
OS (Networking routines)
OS (Networking routines)
Programs
Programs
Suggests universal form
of communication.
Suggests universal form
of communication.
Protection & Security
Protection & Security refer to a mechanism for controlling access by programs, processes,
or users to both system and user resources
The protection mechanism:
 When several separate processes execute concurrently, it should not be
possible for one process to interfere with the others or with the operating
system itself
The security mechanism must:

distinguish between authorized and unauthorized usage

specify the controls to be imposed (conditions to access)

provide a means of enforcement (reject access)
OS (Protection Mechanism)
Processes
Authorized
Rejected
Users
Resources
Command Interpreter
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One of the most important systems programs for an operating system is the command
interpreter,
which is the interface between the user and the operating system.
Some operating systems include the command interpreter in the kernel.
Other operating systems, such as MS-DOS and UNIX, treat the command interpreter as a
special program that is running when a job is initiated, or when a user first logs on (on timesharing systems).
Users
Users
Command
Interpreter
(Shell)
OS
Implementation of System Calls
• System calls are the way of activation the OS appropriate components from the
user programs.
• grouped roughly into six major categories: process control, file manipulation,
device manipulation, information maintenance, communications, and protection.
Passing of parameters
Three general methods are used to pass parameters to the operating system.
 The simplest approach is to pass the parameters in registers. In some
cases, however, there may be more parameters than registers.
 In these cases, the parameters are generally stored in a block, or table, in
memory, and the address of the block is passed as a parameter in a
register.
 Parameters also can be placed, or pushed, onto the stack by the program
and popped off the stack by the operating system.
Some operating systems
prefer the block or stack
method because those
approaches do not limit the
number or length of parameters
being passed.
System Calls Example
As you can see, even
simple programs may
make heavy use of the
operating system.
Frequently, systems
execute thousands of
system calls per
second.